Orienting mechanism for magnetic detector devices



March 24, 1953 P. M. MURPHY 2,632,884

CRTENTING MECHANTs-M ECR MAGNETIC DETECTOR DEVICES Filed June 11, 1946 5 Sheets-Shea?l l March 24, 1953 P. M. MURPHY ORIENTING MECHANISM FOR MAGNETIC DETECTOR DEVICES Filed June ll, 1946 Ewii 31e/IMM March 24, 1953 P. M. MURPHY 2,632,884

ORIENTING MECHANISM FOR MAGNETIC DETECTOR DEVICES Filed June 11, 1946 5 Sheets-snee?. 15

lMMur/Uhy HMM/Wulf March 24, 1953 P. M. MURPHY 2,632,884

ORIENTING MECHANISM FOR MAGNETIC DETECTOR DEVIGES Filed June l1, 1946 5 Sheets-Sheet 4 F556. 72 79 il? 78 3a 5 as 8 87 33 a7 e5 es EM Murphy March 24, 1953 P. M. MURPHY 2,632,884

' ORIENTING MECHANISM FORMACNETIC DETECTOR DEVICES Filed June 11, 194e x 5 sheets-Sme*v 5 gmc/nm JMMur/Uhy Summa;

Patented Mar. 24, Y 1953 UNITED STATES PATENT i OFFICE ORIENTING MECHANISM FOR MAGNETIC DETECTOR DEVICES (Granted under Title 35, U. S. Code (1952),

sec. 266) 7 Claims.

This invention relates generally to orienting mechanisms and more particularly to an orienting mechanism for an airborne magnetic eldsensing element adapted to maintain .the element in a predetermined position with respect to an ambient iield as the supporting body therefor changes position.

The device of the present invention is specially adapted for use with a magnetic airborne detector of the type disclosed and claimed in the copending application of Gerhard O. Haglund for Aerodynamic Body, Serial No. 671,341, led May 21, 1946, now Patent No. 2,551,596.

` The magnetic airborne detector, hereinafter referred to as MAD, is a recording total field magnetometer adapted to be employed in conjunction with an aircraft for the purpose of detecting magnetic anomalies caused by the presence of submarines, sunken ships, magnetic ore deposits and the like. The detector element of the MAD comprises -three coils arranged with their axes mutually perpendicular. One of the coils is selected as the detector coil and is adapted to be maintained in alignment with the lines of force of the earths magnetic field by certain control apparatus such, for example, as servomotors Whose operation is initiated in response to the detection of a field by the remaining two coils.

In devices hitherto known or used for the purpose of orienting the coils, it has been the usual practice to mount the coils in a gimbal support in which the detector coil is directed by rotation about two mutually perpendicular axes. The main axis of such a gimbal could be either horizontal longitudinal, horizontal transverse or vertical. In practice, however, it has been found that neither one of the above arrangements of the main axis is entirely satisfactory for all conditions of operation. The principal disadvantage arises as the detector coil approaches within substantially ten degrees of the main gimbal axis in response to movement of the towing aircraft. When this occurs, the speed of rotation required of the servomotors to align the detector coil with the lines of force of the earths magnetic field 1s iive times as great as that of the motion being followed. As the angle between the detector coil and the main gimbal axis decreases toward zero degrees, the speed ratio increases toward infinity such that at a certain angle, the motors are unable to align the detector coil with the lines oi Iforce and spurious signals will result.

The foregoing undesirable condition also exists when the towing aircraft maneuvers in such a way as to place the main gimbal axis within ten degrees of the magnetic dip angle of the earths magnetic eld and is usually produced by the banking or pitching or" the aircraft. During maneuvers which are incident to submarine searching or geophysical surveying with the MAD, it is necessary to be able to turn about rapidly and return as quickly as possible to the target area after each pass thereover and in executing these rapid turns steep angles of bank are involved extending from forty degrees in larger planes to as high as sixty degrees in smaller planes. Therefore, the utilization of prior art devices is limited to certain latitudes and certain small angles of bank therein,

The gimbal support of the present invention obviates this disadvantage by automatically moving the main gimbal axis away from the detector coil whenever the coil tends to approach the main gimbal axis. This is accomplished by introducing into the gimbal support a third gimbal member rotatable about an axis in the same plane of and at right angles to the main gimbal axis which is selected as horizontal athwartship. The added gimbal member is coupled to the gimbal member which supports the detector coil such that rotation of the detector coil through an angle B, for example, in order to align the coil with the earths magnetic iield also causes the main gimbal axis to rotate through an angle of 1/2 B with respect to the coil whereby the alignment of the main gimbal axis with the coil and the consequent generation of spurious signals are avoided.

It is an object of the present invention to pro vide a magnetic airborne detector in which the total eld coil is maintained in alignment with the lines of force of the ambient magnetic field under all conditions of operation.

Another object is to provide a new and im proved orienting mechanism for an MAD and in which the main axis thereof is prevented from aligning with the total iield coil.

vention and showing the orienting mechanism in A elevation;

Fig. 3 is a horizontal sectional view through the supporting body;

Fig. 4 is a vertical sectional view through the gimbal assembly associated with the orienting mechanism;

Fig. 5 is a view in section taken substantially along the line 5-5 of Fig. 4;

Fig. 6 is a sectional view taken substantially' along the line 6-6 of Fig. 4; I

Fig. 7 `is a sectional viewr taken substantially alongthe line l-l of'Fig'. 6;

Fig. V8 is a view in section taken substantially along the line 8-8 of Fig. 6; and,

Figs. v9 and 1'0 illustrate `diagrammatically the relative motion between lthe gimbals comprising the gimbal assembly.

Referring now to the drawings wherein like characters of reference are employed to designate like parts throughout-the severa-1 views, and more particularly to Fig. 1 thereof, the numeral Illy generally designates a stabilized airborne body adapted to support `the detector element and orienting mechanism therefor of the magnetic airborne detector. IThe body'or'bird I'l` is adapted; to be suspended from and towed by a suitable aircraft I I bymeans of a dual purpose cable I2 in order that themagnetic'eld of the towing aircraft will not influence the detector element.

Fig. l illustrates the application of the MAD to searching and tracking of va submerged sub'- marine I3;

The bird I is provided Vwith a pair of internal grooved segments I4 and I5 `by means of' which a frame comprising a pair of parallel rods is and'I 1, preferably composed of aluminum, is supported within the bird, supporting pins it and .I9 extending from rods I@ andv I'I and being adapted to engage the grooved segments isi and I`l respectively. vIn order to maintain the rods in predetermined space relation, a ring member 2I is aiiixed to the rearward ends of the rods, the ring being adapted to abut against the reduced end portion of the'bird IU. A suspension gimbal assembly, indicated generally by the numeral 22 is lsecured to a mounting plate 23,.the plate 23, in turn, 'being secured to the rods I5 and I'I. Secured to the innermost gimbal of assembly y22 is the male portion 2li of a plug connecter which is carried by cable i2 adapted to receive the female portion 2.5 of the connecter whereby the birdv and apparatus supported therein is suspended by and towed from the aircraft I I. The plug yconnecter is of a type adapted to provide 4a suspension means and-a means for transmitting electrical power to various electrical devices comprising the orienting mechanism of the presentinvention, a-swill appear in more detail hereinafter, and for a more complete description thereof reference is made to the copending applicationzof E- O. Schonstedt for Anchoring Means for Strain Cored Electrical Cables. Serial No. 674,408,1iled June 5, 194.6, now Patent No. 2,590,131. The bird .is providedlwith 4 an opening 26 through which the cable I2 extends, a boot 2'! being fitted around the cable and afxed to the bird in order to prevent rain, dust and the like from entering the bird.

A support 28 for the gimbal mechanism is secured to the rods i6 and il as by bolts 29 and is adapted to engage a shoulder I formed integral- 'ly on the inner periphery of the bird. Support 423 is secured to the bird by any suitable means such, for example, as snap-slide fasteners 32.

The gimbal mechanism comprises three ele- .ments, the outermost gimbal being in the form of a U-shaped member 35, rotatable about the longitudinal axis of the bird. Member 33 is rotatably supported within an opening 34 in support 28 by a hollow cantilever type bearing 35 provided 'with suitable ball bearings 36. The

intermediate gimbal is in the form of a substan- '.tially rectangular member 31 rotatably mounted in suitable hollow bearings 38 carried by member 33. The axis of rotation of member SLhereinafter referred to as the main gimbal axis, is disposed at right angles to the axis of rotation vof member 33. The innermost gimbal vis Vin the form of a substantially cylindrical member 39, hereinafter referred to as inductor mounting,Y rotatably vmounted preferably in pin type bearings 4I carried by member 31. The axis of rotation of member S39 is dispo-sed at right angles to the main gimbal axis.

Inductor mounting 39' is provided With an opening i2 therethrough in which detector coil 43 is mounted, suitable eddy current shields, M being arranged over the ends thereof. Additional openings 45 and 46 are provided in the mounting 39 in which transverse coil' 41 and axial coil d8 are arranged, respectively. Suit.- able adjusting screws 49 are also providedin .order that coils 7 and 8 properly may be .arranged rwithin the openings individual thereto..

A drive unit, indicatedv generally by numeral 5I, is adjustably secured to rods I 6 and IL'I .at the rear portion thereof and comprises. a transverse motor 52 and an axial motor '53.. The vmotors preferably are of the servo. type. and are adjustably mounted in order that their lmagnetic influence on the detector coil may bereduced to a minimum. The outermost gimbal member 3'3 is driven about the axis .of rotation thereof by means of a flexible drive cord 5'4 which passes around a pulley E secured to gimbal 33- byscrews 55. Each end of cord 54 is. secured to one end of a tensioning spring El' individual thereto. the other end of the springs being anchored within av hole in pulley 55. whereby the cord is maintained in a taut condition.

From pulley 55, drive cord 54. passes through a. pair vof guide rollers 53 supported by brackets 59 secured tosupport 29;, from whence the. cord extends through an opening in support 28 to capstan 6| associated with the transversey motor 52. The cord is looped around the capstan -and is returned to pulley 55 through lanotheropeil'- ing in support 28 Yand over two-additional guide rollers E52 supportedY in la manner Asimi'la'r'tothat of rollers, y A

The intermediate gimbal 37 is provided 'with two grooved segments 63 and 613 secured thereto as vby screws S5 and which are adapted Sto receive a fiexible .drive cordv 6 6 by means of which the gimbal 3l is actuated. The endsof cord 66 `are respectively secured to tensioningsprings '61, vthe springs, in turn, being anchored in thesegments 63 and EB.. Cord 65 extends from thels'egments Aover idler pulleys 68 secured to gimbal 33 and adapted to direct the cord through the hollow bearing 35 about which gimbal 33 rotates, therelby preventing the rotation of gimbal 33 from interfering with the rotation of gimbal 31. Cord `56 continues over additional idler pulleys 69 adapted to guide the cord in such a manner that it properly will pass over capstan 1l of axial motor 53, idler pulleys 99 being secured to rods I 6 and l1 in any suitable manner.

The innermost gimbal member or inductor mounting 39 is rotated by means of cords 12 Tand 13 which extend from a double grooved pulfley 14 rigidly secured to support 28 by screws '.15. Pulley 14 is of the same diameter as the inductor mounting and is arranged on support 28 coaxially with the axis of rotation of gimbal 33. One end of cord 12 is secured to a tensioniing spring 16 which, in turn, is anchored within one groove of pulley 14. From spring 16, cord 12 extends over idler pulleys 11 and 18, supported on brackets 19 secured to gimbal 33, from whence it passes through the hollow bearings 38 'carried by gimbal 33 and over an additional vidler pulley 8i rotatably supported within gimbal 31. The mounting 39 is provided with an opening 82 adapted to receive a plug 83 whose 'function is to pin cord 12 within the opening, the cord passing from pulley 8| around the under Aportion of mounting 39 to opening 82.

Similarly, one endof cord 13 is secured to a ntensioning spring 84 which, in turn, is anchored within the other groove of pulley 14. From pulley v14, cord 13 extends as follows: over idler pulleys 85 and 88 supported on brackets 81 secured to gimbal 33, through the other hollow bearing 38 on gimbal 33, over an additional idler pulley 88 'rotatably supported within gimbal 31, from whence the cord passes around the under portion of mounting 39 to the opening 82 therein i 'where it is pinned by plug 33. Cord I2 continues from opening 82 forwardly across gimbal 33 and is secured thereto by clamp 89, cord 13 also ex- -tending from the opening rearwardly across gimbal 39 and being secured thereto by a clamp 9|.

Cords 12 and 1,3 preferably are of the tinsel conductor type whereby electrical connection to the coils 43, 41 and 48 is effected, cord 12 having three conductors disposed therein and cord 13 vvhaving two conductors disposed therein. Each conductor is terminated at a terminal block 92 located on support 28. Suitable cables extend Afrom the terminal block and together with the cables extending from motors 52 and 53 are secured to the male portion 24 of the plug con- 'nector hereinbefore described.

As heretofore described, the main detector coil is adapted to be maintained in alignment with the direction of the lines of force of the earths magnetic eld such that the transverse and axial coils are disposed at right angles to the vdirection of these lines of force. Both the transverse and axial coils are excited with a voltage of predetermined frequency supplied from a suitable alternating current source comprising the control apparatus of the MAD, indicated generally by numeral 93 and located in the aircraft l l. As either of these coils forms an angle of less than ninety degrees with the lines of force lof the earths field, there will be induced therein a second harmonic voltage of a magnitude and fphase depending upon the magnitude and direc- "tion of the angular displacement of the coil. The second y harmonic voltages are transmitted through cable l2 to control apparatus 93, wherein the voltages are converted in frequency andthe converted voltages are thereafter applied to the driving motors associated with the coils.

Displacement of the transverse coil 41 initiates the operation of transverse motor 52 to rotate the outer gimbal 33 in either direction to correct for the displacement. The foregoing arrangement of cords 12 and 13, it will be noted, has the same effect as an endless cord passing over pulley 14 and around the inner gimbal`39 thereby coupling together the outer and inner gimbals such that the rotation of gimbal 33 about its axis of rotation causes the inner gimbal to rotate in the same direction as, and through twice the rotational angle of, the outer gimbal. Such an arrangement prevents the main detector coil from approaching within ten degrees of the main gimbal axis and, hence, from aligning with the main gimbal axis. -By Way of example, let' it be assumed that the aircraft Il is in level flight at the equator. Under this condition, an angle of forty-five degrees exists between the main detector coil and the main gimbal axis. If, then,

.the aircraft executed a forty-five degree bank,

the angular difference between the main detector coil and the main gimbal axis would be twentytwo and one-half degrees, well beyond the critical ten degree region.

Fig. 9 illustrates the relative positions of the gimbals while the aircraft is in level iiight at the equator, A-A representing the axis of the main detector coil, B B the main gimbal axis, and C-C the horizontal athwartship axis of support 28. Fig. 10 illustrates the relative positions of the gimbals while the aircraft executes the forty-five degree bank of the aforementioned example. From an inspection of these views, it can be seen that if the outer gimbal is rotated through an angle e, for example, with respect to support 2S, the inner gimbal 39 is caused to rotate through an angle of a with respect to the outer gimbal, or through an angle of 2a with respect to support 28.

Displacement of the axial coil 48 initiates the operation of the axial motor 53 to rotate the intermediate gimbal 31 in either direction to cor- 'rect for the displacement.

It is well known that the direction of the lines of force of the earths magnetic eld in the Asouthern hemisphere is opposite to those in the northern hemisphere.

.ing 94 is provided in the inner gimbal diammetrically opposite opening 82 and to make the change plug 83 is removed from hole 82, the inner gimbal is rotated degrees and the drive cords 12 and 13 are pinned in opening 94. Also, the driving cord 86 is crossed in order to compensate for the fact that the voltage generated by the axial 'coil'in the southern hemisphere is oppositein 'direction from that generated thereby in the northern hemisphere.

It will be noted that, with the exception "of Asupport 28 which preferably is composed of fibre block, the gimbal assembly of the present orient,- ing mechanism is constructed chieiiy of Lucite to avoid the use of metals and at the same time .avoid dimensional changes resulting from humid- 'ity changes.

From the foregoing, it should now be apparent .that anyorienting mechanism has been provided which-Ils: well adapted to fulll the aforesaid objects of the; inventionL While the invention has been disclosed in particnlarityV with reference to` an example thereof which gives satisfactory results, it readily will be apparent to those skilled in the art to which the invention. appertains, after understanding the invention, that further changes, modifications and embodiments may be made without departing; from the spirit and scope of the invention as defined by the claims appended hereto.

The present invention may be manufactured and usedby or for the Government of the United States of America for governmental. purposes .without payment of any royalties thereon or therefor..

vWhat is claimed as new and desired tobe secured by Letters Patent of the United States is:

1i InI a device for detecting anomalies in the earths` magnetic iield, three gimbal members rotatably supported one within the other,` three field. sensing elements carried by the innermost gmbal member and having. their axes of sensitiyity disposed mutually perpendicular, the axis of. sensitivity of one of said elements having an initial predeterminedV position in alignment with thedirection-of the. earths magnetic iield, means individual to the two outermost gimbal members andr respectively controlled by the other of said 'elements for causing rotation of thetwo outermostgimbal members as said one o1" the elements deviates from said initial predetermined position, and means effective as the outermost gimbal memberv rotates to cause the innermost gimbal member to rotate through an angle twice that traversed by the outermost gimbal member.

2; An orienting mechanism of the character disclosed comprising, in combination, a pair of `girnbals rotatable about mutually perpendicular axes, a magnetic eld sensing element carried by f one of said pair of gimbals and having its axis normally in alignment with an ambient magnetic eld, and means for causing the rotational axis of the other of said pair'of gimbals to recede when the axis of said element moves in the direction thereof.

3. In a system including a moving veln'cle for detecting the presence of material having a localized magnetic field, a hollow body to be Carried hy'saidmoving vehicle and to be electricallyr connected to motor control apparatus mounted within said vehicle, a plurality of gimbal mountings carried within said body, one of said gimoal mountings containing a detector coil, a transverse coil,r and an axial coil mounted therein and adapted for electrical connection to and control of, said control apparatus, at least one electric motor mounted within said body and adapted for electrical connection to said control apparatus and. having mechanical connections with said gimbal mountings to produce a particular rota.- tion required thereof about their respective axes .under control of said control apparatus in response to the detection of a magnetic eld by said coils and thereby maintaining said detector coil in alignment with the magnetic eld of the earth, one of said' mechanical connections providing a two tov one ratio of movement to said one of said Vgin-:bal mount-ings with respect to another of said gimbal mountings whereby the coils are rapidly moved to a required position.

- 4. A- movable orienting mechanism for a magnetic detection device comprising a plurality of gimbals, one of said gimbals containing a pluirality of magnetic detection coils mounted 'inutumlyperpendlcularto. one another within said one gimbahmeans electrically connected to. said coils and comprising prime mover means having mechanical and rotative connections to each of said gimbals whereby a` particular rotation. of each gimbal. is eilected relative to eachv of. the otherv gimbals in response to the detection of a magnetic field by said coils to maintain one of said coils. in alignment with the lines of force of the earths magnetic neld. as the mechanism is moved angularly with respect thereto, said mechanical and rotative connections between said one gimbal and one of said other gimbals rotating said oney gimbal through an. angle twice that traversed by said one of said other gimbals as rotation thereof is produced by said electrical means.

5. Apparatus of the character disclosed comprising, in combination, a casing member, an electricalsocket element carried by said casing member to receive electrical plug element on one end of an electrical towing cable electrically connected to an electric motor control apparatus mounted within a towing vehicle, a plurality of gimbal mountings carried within said a detecting coil mounted within one of said gimbal mountings and 'perpendicular to the axis of rotation. of said gimbal mounting, a transverse detecting coil mounted within said one gimbal mounting and perpendicular to the axis of rotation of both said one gimbal mounting and said iirst mentioned detecting coil, an axial detecting coil mounted within said one gimbal mounting and perpendicular to said iirst and second mentioned detecting coils and in substantial aligninent with. the axis of rotation of said one gimbal mounting, an electric prime mover mounted transversely within said casing and elec.- trically connected to said socket element., an axial electric prime mover mounted within said casing and electrically comnected to said socket element, electrical connection means connecting said coils to said socket, means including a plurality of pulleys mounted on said prime movers and gimbals, respectively, and a plurality of cables cn said pulleys for mechanically connecting said primev movers to said g'rnbal mountings. thereby to effect rotation thereof in such a manner that the first mentioned detector coil is maintained in alignment with the magnetic eld oi the earth by rotation of said first mentioned coil through an angle which is twice as large as the angle through which another of said gimfbal mountings is rotated.

6. A total field magnetometer of. the character disclosed comprising, in combination, a casing, a plurality of gimbal members. carried within said casing, three mutually perpendicular mag.- netic detecting coils carried by one of said gimbal members and electrically connected to a plurality of terminals upon said casing, electrical means for rotating said gimbal members through mechanical connections, said mechanical connections including a coupling between another of said gim-bal members and said one gimbal member whereby said one gimbal member is caused to rotate through an angle twice that traversed by said other gimbal member as rotation thereof is producedr by said electrical rotating means.

7; in a device for detecting anomalies in the magnetic neld oi the earth, a plurality of gimbal members, a plurality of magnetic iield sensing 'elements carried by one of said gimbal members with the axes of sensitivity of said sensing elements disposed in mutually perpendicular relationship, the' axis of sensitivity of one of said sensing elements being positionable in alignment with the flux lines of an ambient magnetic field, electrical means including the other sensing elements having mechanical connections to said gimbal members to cause rotation of each girnbal member relative to each other gimbal member upon movement of said one Isensing' element out of said alignment whereby said one sensing element is maintained in substantial alignment with said ambient magnetic field, said mechanical con- 10 nections including a coupling between another of said gimbal members and said one of said gimbal members whereby the sensing elements are caused to rotate through an angle twice that traversed by said other gimbal member as rotation thereof is produced by said electrical means. 1

PAUL M. MURPHY.

10 REFERENCES CITED The following references are of record in the i'lle of this patent:

UNITED STATES PATENTS Number Name Date 1,716,484 Carrey 1 June 11, 1929 2,414,128 Sinks Jan. 14, 1947 2,488,341 Slonczewski Nov. 14, 1949 OTHER REFERENCES Air-Borne Magnetometers. From Electrical Engineering. Pp. S80-685. July 1947. 

